Struct FormViewSpec 

pub struct FormViewSpec<'a> {
    pub title: &'a str,
    pub subtitle: Option<&'a str>,
    pub fields: &'a [FormField],
    pub banner: Option<(&'a str, Color32)>,
    pub trailing: Option<&'a [(&'a str, Vec<String>)]>,
    pub extra: Option<(&'a str, &'a dyn Fn(&mut Ui))>,
    pub exit_label: &'a str,
    pub rollback: bool,
    pub hits_prefix: &'a str,
}

Everything ABOUT the form that the consumer supplies. Borrowed; the form view holds no state of its own beyond egui memory.

Fields

title: &'a str

The form’s heading — e.g. "E3 ⟠ Extrude". Also the scope key for this form’s transient view state and per-field widget ids, so it must be STABLE and UNIQUE per subject (a feature id / constraint id qualifies).

subtitle: Option<&'a str>

An optional second line under the title (a status, a type name…).

fields: &'a [FormField]

The schema fields to render, in schema order.

banner: Option<(&'a str, Color32)>

A message banner drawn under the title — e.g. the feature’s run error.

trailing: Option<&'a [(&'a str, Vec<String>)]>

Read-only sections appended after the fields — e.g. [("Outputs", …)].

extra: Option<(&'a str, &'a dyn Fn(&mut Ui))>

ONE consumer-drawn section (title, drawer) placed after the schema groups and before the trailing sections — for a subject whose editing surface the schema cannot express (a spline’s anchor list). The drawer is Fn, so anything it decides goes through interior mutability the consumer owns; the form view stays intent-out like everything else here.

exit_label: &'a str

The exit button’s label — the button at the RIGHT end of the title row. Both of today’s consumers say “Return to tree” — the history feature list and the constraint list are BOTH drawn by panels::tree, so the word is literal, not a metaphor (Q12). A consumer whose list is NOT a tree supplies its own wording here.

rollback: bool

Whether this consumer’s subject lives in a ROLLED history — i.e. whether LEAVING the form also means “roll the model back to the tip”.

The form view holds no engine and therefore cannot roll anything itself (that is FormViewOut::roll_to_tip, which the caller acts on). What this flag does is decide, in ONE place, whether an exit carries that intent — so no consumer has to hard-code “am I the history panel?” at its exit arm. The history panel passes true; assembly constraints have no rollback at all (the owner’s call) and pass false, which is why their panel has no roll branch to get wrong.

hits_prefix: &'a str

Prefix for every published hit key. "" for a consumer that shows ONE form at a time (history); a consumer that can show several at once MUST pass a prefix carrying the subject id or the rects collide silently.